One of the problems faced by the perfumery industry lies in the relatively rapid loss of olfactive benefit provided by odoriferous compounds due to their volatility, particularly that of “top-notes”. In order to tailor the release rates of volatiles, delivery systems such as microcapsules containing a perfume, are needed to protect and later release the core payload when triggered. A key requirement from the industry regarding these systems is to survive suspension in challenging bases without physically dissociating or degrading. For instance, fragranced personal and household cleansers containing high levels of aggressive surfactant detergents are very challenging for the stability of microcapsules. On the other hand, fine fragrance formulations containing up to 90% ethanol, result in similar phenomena of destabilization and dissociation albeit by different mechanisms, of encapsulated systems added therein.
Aminoplast microcapsules formed of a melamine-formaldehyde resin have been largely used to encapsulate hydrophobic actives, thus protecting said actives and providing their controlled release. However, capsules such as aminoplast ones suffer from stability problems when used in consumer products comprising surfactants, such as perfumery consumer products, especially after prolonged storage at elevated temperatures. In such products, even though the capsule wall remains intact, the encapsulated active tends to leak out of the capsule by diffusion through the wall due to the presence of surfactants that are able to solubilise the encapsulated active in the product base. The leakage phenomenon reduces the efficiency of the capsules to protect the active and provide its controlled release.
A variety of strategies have been described to improve the stability microcapsules with oil core. Crosslinking of capsule walls, with chemical groups such as poly(amines) and poly(isocyanates), has been described as a way to improve stability of microcapsules. WO2011/154893 discloses for instance a process for the preparation of polyurea microcapsules using a combination of aromatic and aliphatic polyisocyanates in specific relative concentrations.
As an alternative to encapsulation, stabilization of oil/water interfaces with inorganic particles has been described in so-called Pickering emulsions. In this context, functionalization of inorganic particles to allow their crosslinking is known. For instance, Pickering emulsions crosslinked from an outer water phase with polyelectrolytes providing electrostatic interactions have been the object of prior disclosures. However, such systems are very likely to dissociate in a surfactant base or in ethanol over time as electrostatic interactions are insufficient to promote stability. Covalent crosslinking has also been described in relation with Pickering emulsion in the preparation of colloidosomes. In particular, the use of diisocyanates as crosslinker has been disclosed in scientific publications. WO2009/063257 also describes the use of polyisocyanates as possible crosslinker for surface-modified inorganic particles in order to prepare microcapsules with increased level of protection from u.v. light for the contents. These products are typically intended for agrochemical applications.
One of the major hurdles in using particle-stabilized capsules for perfume encapsulation intended for fine fragrance and other scented consumer product applications is their inherent instability to ethanol and the ability of surfactant molecules to readily displace particles from oil/water interface of emulsions.
Therefore there is still a need to develop improved delivery systems that efficiently protect and then release, when needed, an active ingredient such as a perfume oil, while surviving suspension in challenging bases without physically dissociating or degrading. A particular need exists in the case of fragranced personal and household cleansers containing high levels of aggressive surfactant detergents and fine fragrance formulations containing up to 90% ethanol. It is an object of the invention to provide such improved delivery systems.